Pulmonary Embolism

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Wells Score & Risk Stratification | Management | Referral

Definition

Pulmonary embolism (PE) is the obstruction of the pulmonary arteries by a blood clot, usually originating from a deep vein thrombosis (DVT) in the legs. It can cause significant cardiovascular and respiratory compromise.

Aetiology

PE is caused by a thrombus, most commonly from the deep veins of the lower limbs (DVT), which embolises to the pulmonary circulation.

Pathophysiology

PE leads to:

  • Increased pulmonary vascular resistance: due to mechanical obstruction.
  • Right ventricular strain: can lead to acute right heart failure.
  • Impaired gas exchange: due to ventilation-perfusion mismatch.
  • Hypoxia: due to reduced oxygenation of blood.
  • Haemodynamic instability: in large PE, reduced cardiac output may cause hypotension and shock.

Risk factors

Risk factors for PE are similar to those for venous thromboembolism (VTE):

  • Immobilisation: recent surgery, long-haul flights, prolonged bed rest.
  • Hypercoagulable states:
    • Pregnancy.
    • Malignancy.
    • Inherited thrombophilias (e.g., Factor V Leiden).
  • Hormonal factors:
    • Oral contraceptive pill (OCP).
    • Hormone replacement therapy (HRT).
  • History of previous PE/DVT.
  • Smoking.
  • Obesity (BMI >30).

Signs and symptoms

Symptoms:

  • Sudden onset breathlessness.
  • Pleuritic chest pain (sharp pain worsened by inspiration).
  • Haemoptysis (coughing up blood).
  • Syncope (suggestive of large PE).
  • Leg swelling or pain (suggesting DVT).

Signs:

  • Tachypnoea (rapid breathing).
  • Tachycardia.
  • Hypoxia (low oxygen saturation).
  • Raised jugular venous pressure (JVP) in massive PE.
  • Hypotension in severe cases.

Investigations

  • D-dimer:
    • Highly sensitive but non-specific.
    • Useful for ruling out PE in low-risk patients.
  • CT Pulmonary Angiography (CTPA):
    • First-line diagnostic test for PE.
    • Directly visualises emboli in the pulmonary arteries.
  • Ventilation-perfusion (V/Q) scan:
    • Used if CTPA is contraindicated (e.g., renal impairment, contrast allergy).
  • ECG:
    • Sinus tachycardia (most common finding).
    • S1Q3T3 pattern (right heart strain, but rare).
  • Chest X-ray:
    • Usually normal but may show features like wedge-shaped infarction (Hampton’s hump).

Wells Score & Risk Stratification

The Wells score helps stratify PE risk:

Clinical Feature Points
Clinical signs of DVT 3.0
PE is the most likely diagnosis 3.0
Heart rate >100 bpm 1.5
Immobilisation ≥3 days or surgery in the past 4 weeks 1.5
Previous DVT/PE 1.5
Haemoptysis 1.0
Malignancy (active or within 6 months) 1.0

Interpretation:

  • Score <4: low risk → Perform D-dimer.
  • Score >4: high risk → Perform immediate CTPA.

Management

1. Immediate Anticoagulation:

  • First-line: DOACs (e.g., Apixaban or Rivaroxaban).
  • Alternative: LMWH followed by warfarin if DOACs contraindicated.
  • Treatment duration:
    • Provoked PE: 3-6 months.
    • Unprovoked PE: consider lifelong anticoagulation.

2. Massive PE (Haemodynamic instability):

  • Urgent thrombolysis (e.g., Alteplase).
  • Consider surgical or catheter-directed embolectomy if thrombolysis contraindicated.

3. Oxygen Therapy:

  • Administer oxygen if SpO₂ <90%.

Referral

  • Respiratory specialist: if PE is recurrent or severe.
  • Hospital admission: if haemodynamically unstable.
 
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